The objectives of this project are to understand the organization, function and evolution of repeated genes and their gene products in tetrahymena. Three repeated gene systems are studied: 1) genes for ribosomal RNA which are found as an independently replicating, extrachromosomal, amplified, palindromic dimer; 2) genes for 5S rRNA which consists of tandem repeats of 120 bp gene and approximately 160 bp spacer; and 3) histone genes, for which there must be at least 7 inner histone types and 4 H1 types. rChromatin will be isolated and its structure and histone composition analyzed. The structure of 5S genes in macro- and micronuclei will be probed utilizing cloned probes, non-specific nuclease digestions, restriction endonucleases and Southern blotting. The role of histones and their secondary modifications in maintaining the structural and functional differences between macronuclei (transcriptionally active, amitotic, somatic nuclei) and micronuclei (transcriptionally inert, mitotic, germinal nuclei) will be studied. Attempts will be made to clone histone gene sequences, whose organization and sequence will be studied.